Thin coatings or films are used for a variety of applications, depending on the coating's mechanical, chemical, optical and electrical properties. High strength, scratch-resistant coatings are highly desirable for any application in which the surface condition is critical to the performance of the device, such as optical components, surgical instruments, and small-scale electrical components. A hydrophobic or hydrophilic coating may be highly desirable for applications in which the device may operate in an aqueous environment such as surgical instruments, or for applications in which it is desired to make the device water repellent, such as electrical devices or vehicle windshields. Anti-reflective coatings are routinely used in many optical devices, and thin fluorescent coatings have many useful applications, such as light-emitting diodes. Thin films with high dielectric constants are routinely used in the fabrication of extremely small-scale semiconductor devices and capacitors as well as electrical surgical instruments.
Various vapor deposition techniques are routinely used to deposit thin layers of material on a variety of substrates, including chemical vapor deposition (CVD) and, more commonly, plasma enhanced chemical vapor deposition (PECVD). Plasma enhanced chemical vapor deposition is a method in which a substrate is placed within a deposition chamber in which two or more reactants in a gaseous phase are injected between two electrical plates powered by radio frequency AC power. The power induces the ionization of the reactants, causing them to react and form new products. The reaction products then accumulate as a solid phase layer on the surface of the substrate. PECVD is especially useful in the fabrication of small-scale electrical devices because the pattern of deposition can be readily controlled with relatively simple masking materials and methods.
Silicon (Si) and silicon-containing compounds are widely used to fabricate coatings on devices using PECVD methods. Crystalline silicon carbide (SiC) is one of the most versatile materials for fabricating electronic devices but requires temperatures of over 1000° C. for fabricating electronic devices. SiC can also be deposited in amorphous or nano-crystalline forms at temperatures as low as 400° C., while retaining useful dielectric properties. Silicon oxide (SiO2) is another material that may be deposited at temperatures as low as 400° C. The lower fabrication temperature makes it possible to deposit the coatings on a wider variety of substrates. Even at 400° C., however, the fabrication temperature may preclude the use of plastic substrates, which melt at temperatures around 200° C. Further, in each of these materials, a tradeoff occurs between the various properties of the coating materials. Crystalline SiC is nearly as hard as diamond, but has a lower capacity to store electrical charge than the other coatings such as amorphous SiC and SiO2. Amorphous SiC and SiO2 have more desirable electrical properties than crystalline SiC, but at the expense of reduced hardness. In addition, the coating materials discussed are limited to a total thickness of about 8 μm due to the cracking and delamination of thicker coatings of these materials. This maximum thickness further limits the potential applications of these materials.
A need in the art exists for a coating material that combines in a single material the separate advantages of previous coating materials. A need exists for a coating material that can be deposited at temperatures as low as room temperature and at much higher thicknesses than existing coating materials. Further, a coating material is needed that simultaneously possesses high hardness values and high dielectric capacity. Lastly, a process of depositing a coating material is needed in which other useful properties such as hydrophobicity or fluorescence may be adjusted to desired levels, without sacrificing any of the other desirable properties of the coating material.